Tube amplifier circuits for electric guitar. Review of Hi-End guitar amplifiers. Basic Control Panel Functions

For some time, having given way first to transistors, and then to microcircuits, radio tubes again returned to the closets of radio amateurs. Currently, these electric vacuum devices have gained great popularity among lovers of good sound. This applies to both musicians and those who listen to their recordings. Numerous companies have responded to the demand and in stores you can now buy a decent amplifier without much hassle, but their cost in some cases is simply astronomical. As a result, many radio amateurs master the basics of building equipment using radio tubes, constructing various amplifiers for their headphones, powerful audio systems and musical instruments. And I didn’t “pass by” when I decided to work on an amplifier for my guitar.

I took a well-proven pre-amplifier circuit as the basis for the future design. Slo Recto Twin designs of Gishyan *AZG* Aznaur, well-known in the circle of tube musical equipment enthusiasts. To the “pre” I added a push-pull power amplifier based on 6P3S beam tetrodes, a delay circuit for the supply of anode voltage and switching with a footswitch.

Schematic diagram

Structurally, the amplifier consists of a pre-amplifier using VL1-VL3 tubes, a push-pull power amplifier (VL4-VL6 tubes) and a common power supply.

The preamplifier, in turn, consists of two channels - clean (clean) and overload ( distortion) with separate tone and volume controls.

The signal from the guitar pickups is fed to the grid of one of the two triodes of the VL1.1 lamp, which is a common amplifier for both channels. In the cathode bias circuit of the triode, using one of the groups of relay contacts, the electrolytic non-polar capacitor C1 is switched, which is included in the circuit in pure sound mode and expands the band of amplified frequencies in the low-frequency region. In overload mode (the relay is activated), it is isolated by the high resistance of resistor R3, so only capacitor C2 remains, which has a relatively small capacity. At the same time, the gain of the cascade is noticeably reduced at low frequencies, which prevents the “booming” of the sound.From the anode of the triode, the signal is divided into two channels. The top one operates in the mode of amplifying pure sound, the bottom one is in overdrive. Channelcleanrepresented by three-lane (treble- high, bass- low, middle- medium frequency) with a tone control assembled according to a fender circuit and an amplification stage on a VL1.2 triode.

Overload ( distortion) has already been implemented by a much larger number of lamps and passive elements. Three cascades based on VL2.1 triodes, VL2.2 and VL3.1 have a large overall gain, due to which the sound is greatly distorted. This creates an effect with a characteristic heavy and powerful sound. To coordinate these stages with the tone control, as well as to prevent mutual influence, a cathode follower on the VL3.2 triode is included in the circuit. In pure sound mode, the overdrive channel is blocked by shorting the VL2.2 triode grid.

To separately regulate the signal level of the cascades, each of them is equipped with variable volume resistors R11 and R38. In addition, there is a general volume control R40 master volume. The engines of all volume controls are shunted with fixed resistors with a resistance of 2.2 megaohms. They are necessary to eliminate possible rustling noises caused by wear of the conductive layer. In themselves, they are not terrible, but in this case the mesh is separated from the common wire, as a result of which the volume of the rustling becomes very loud.

The amplified and processed signal from one of the channels is fed to the input of a differential phase inverter assembled on a VL4 lamp. Its task is to additionally amplify and create two identical signals at the output with a phase shift of 180 ° relative to each other for the operation of a push-pull power amplifier using 6P3S lamps.

Switching of the pre-amplifier channels is carried out using two relays, which, in turn, are switched using a footswitch (you can select the desired channel by pressing the foot of a button, like in a lotion) or a switch on the front panel. There are also mode switches bright(S1) and treble shift(S2) to change the sound color of each channel. The indicator LED VD13 in the footswitch is included in the circuit of switching relays and lights up when the S6 button is pressed to turn on the channeldistortion. Capacitor C57 with a relatively large charging current at the moment the button is pressed ensures reliable operation of the relay, since the current flowing through the LED may not be enough for this.

The amplifier is powered by a transformer power supply with passive anode voltage filtering with a delay circuit, and with a 12AX7 lamp filament voltage stabilizer. The anode voltage rectifier uses ultra-fast UF4007 diodes, thanks to which it is possible to almost completely eliminate the switching noise of diode switching. To ensure that power is supplied to the lamps only after their cathodes have warmed up, the amplifier uses a delay circuit assembled on transistors VT3 and VT4. Relay K3 is activated approximately 10-15 seconds after the amplifier is turned on (selected with capacitance C55) and closes contacts K3.1. The filaments of the pre-amplifier lamps are powered by a stabilized voltage of 12.6 volts to reduce background and noise, as well as to increase the service life of these vacuum devices. The voltage at the cathode of the VL3.2 repeater is quite high due to the high resistance of resistor R33, because of this a significant potential difference is created between the cathode and its filament, which greatly reduces the operating time of the lamp. To neutralize this effect, the filament potential “rises” relative to the common wire by approximately 75 volts. The corresponding voltage is supplied from the divider R67 and R68 to the symmetrical filament divider R65 and R66. The same divider is installed in the filament circuit of the output lamps (6.3 volts), but its middle point is connected to the common wire.

The ground decoupling is made according to the “star” scheme, when the wires from the common wire circuits of different stages are connected at one point and have reliable contact with the amplifier body.

Details

All amplifier fixed resistors must be metal film (MF) or metal oxide (MO). They have less noise, unlike carbon CF resistors. Domestic MLT resistors are also suitable.

Film capacitors must be of the MKP series from Wima or Epcos for a voltage of at least 400 volts. These "musical" capacitors are quite common. You can also use good domestic K71 series. Consumer-grade K73 produces slightly worse results. You should beware of old metal paper capacitors such as MB or MBM. As a rule, even the “newest” copies are more than 30 years old and almost all of them have significant leakage currents. Electrolytic capacitors are best used with a maximum operating temperature of 105 degrees due to their proximity to hot lamps. For capacitors in anode circuits, the voltage must be at least 400 volts. The 0.022 μF capacitors shunting them must be of type X2, designed to operate in an alternating voltage circuit of at least 275 volts. Their operating DC voltage is 600-1000 volts, and their low internal resistance to pulse current contributes to good filtering of noise and ripple. Instead of non-polar electrolytes C1 and C10, conventional polar ones can be used. For small-capacity capacitors in tone blocks and in the bass reflex, it is better to take film, mica from the KSO and SGB series or imported high-voltage blue ceramic capacitors.

The preamplifier uses Russian-made 12AX7 tubes from Tung Sol. You can use them instead ECC83 or domestic 6N2P-EV. In this case, the filament voltage should be reduced to 6.3 volts. To do this, you need to replace the VD9 zener diode with another one - with an operating voltage of 3.3 volts. With some deterioration in sound quality, you can use 6N2P, 6N23P and even 6N9S, as well as other double triodes. Common domestic 6P3S tetrodes are used as output lamps.

Transistors in the delay circuit, as well as VT2 in the filament stabilizer of the preliminary lamps, can be any silicon low-power n-p-n structures and with a minimum emitter current transfer coefficient of 100. For example - KT315, KT3102, SS9014 and so on. Powerful transistor VT1 must have a maximum collector current of at least 4 amperes and a maximum voltage of at least 100 volts. If its body is not insulated (TO-220FP), then it should be attached to the radiator through an insulating heat-conducting gasket "Nomakon", and the tightening screw should be equipped with a plastic washer.

It is advisable to use ultra-fast diodes in the anode rectifier VD1-VD4, such as UF4007, but you can also install regular rectifiers with a maximum reverse voltage of at least 600 volts and a forward current of 1 ampere. In this case, each of them is shunted with a film or ceramic capacitor with a capacity of 0.01 μF to a voltage of at least 630 volts. Diodes VD5-VD8 with a Schottky barrier, they can be replaced with any with a maximum forward current of at least 3 amperes.

I used specialized relays for switching audio signals - 46ND012-P from FUJITSU . But you can use any with an operating voltage of 12 volts, with two switching groups and minimum operating current.

Transformers and chokes are homemade. The first ones are wound on frames and cores from the Russian Corvette computer manufactured in the mid-90s. Their U-shaped tape magnetic cores have a small dispersion field and can be installed without magnetic shields. Any transformer iron with a cross-section of 6 cm 2 is also suitable. Data on windings and voltages are given in the table in the diagram. Between the layers, one layer of varnished cloth or thin capacitor paper should be laid, and between the windings the number of layers should be at least three. Between the halves of the magnetic cores there are insulating pads made of varnished cloth, 0.3 mm thick. The chokes are wound with 0.25mm wire until the frames are filled. Their cores must have a cross-section of at least 2 cm 2 with a dielectric insulator between their halves.

Design

Attention! This amplifier, like most other tube devices, contains high voltage that is dangerous to life and health, so all installation work and adjustments should be carried out in compliance with safety precautions!

Structurally, the amplifier is made on an open duralumin chassis, repeating the design approach to the design of tube audio amplifiers. Variable resistors, almost all connectors and switches are mounted on the front panel, which has an easy-to-use bend at an angle of 45 degrees. The sockets for fuse FA1 and the output of the audio transformer, as well as the power connector, are located on the rear wall.

The footswitch is assembled in a separate durable case, connected to the amplifier with a long cable.

The printed circuit board is quite long, so the thickness of the foil fiberglass laminate must be at least 3 mm to prevent unnecessary deformation. if you cannot find such material, then you can use the common one with a thickness of 1.5 mm, but you must provide holes for attaching the stands in the middle of the board.

Setup

Despite the rather large complexity of the circuit, the amplifier begins to work immediately after switching on, if, of course, all the parts used in it are in working order. However, the operation of the device should be checked step by step. First, the amplifier is turned on without tubes and the operation of the delay circuit is checked. Next, by adjusting the tuning resistor R63, the filament voltage of the pre-amplifier lamps is set to 12.6 volts. Next, with the lamps, you must again adjust this voltage, which will “fall” under load. After this, the voltage on the anode supply capacitors is measured. It should be 330-360 volts. It should be noted that for a working amplifier these figures will be lower.

Next we insert the power amplifier lamps VL4-VL6 into the corresponding sockets. A shielded wire is temporarily soldered to the upper terminal of the variable resistor R40 in the diagram, the second end of which can be connected to any audio source - a player or mobile phone. At the same time, clear, undistorted music should be heard in the speakers. Next, insert the VL1 lamp into the sockets and connect the guitar to the input of the amplifier, which is switched to the “clean” channel. Make sure it works well. Then they insert the remaining lamps and check the channel distortion

The lamp modes are selected optimal, and they remain so when using resistors with a standard tolerance of ±5%, so no selection of elements is necessary.

Together with this amplifier, I use a cabinet (“speaker” for guitar amplifiers) with a Vintage 30 speaker from Celestion installed in it. It is not recommended to install conventional speakers used in car and household speaker systems, since it is the guitar speaker with its special frequency response shape (mid-frequency rolloff) that creates the special sound of an electric guitar.

List of radioelements

Real tube sound

Hello! Today we'll talk about the most important part of guitar sound - the tubes in the power amplifier! They greatly influence how the amplifier sounds, and specifically on such sound parameters as tone, volume, power, and overdrive quality. When choosing an amplifier, it is important to understand how certain lamps differ from each other; I hope that this article will help you better understand this issue. The 4 main types of tubes used in guitar amplifier terminations are 6L6, EL34, 6V6, and EL84. There are also others, such as KT66 or KT88, but if you understand the differences between the 4 main types, you will understand more about the differences between other lamps that are not so common.

End section

So, let's start with the basic concepts. A guitar amplifier consists of 3 main parts: a preamp (preamplifier section), a power amplifier (also known as the power amplifier) ​​and a power section (the transformer and everything after the power amplifier). The rectifier tube in the power section has a significant effect on the sound. It is also very important which tube is placed first in the preamplifier (in place of v1). But today we are not talking about them, but about the lamps responsible for power and volume - about the lamps in the terminal. They not only amplify the signal coming to them from the preamplifier, but also add their own characteristic overdrive and frequency coloring to the sound. In my opinion, the end tubes play the most important role in how an amp ends up sounding. It is because of the differences in the terminal lamps that such characteristic terms as American and British sound, as well as various other subspecies and varieties, appeared.

Imagine this: most hi-gain amplifiers have a gain knob that controls the overdrive on the channel. Next comes the master volume knob so that we can adjust the level that is convenient for us. Thus, it turns out that we can play with overdrive and at low volume. The overdrive that you hear in this case is the overload of the preamp tubes. As a rule, the sound itself is quite fuzzy, curly (depending on the amplifier) ​​or grainy, the return from this sound is very small, it is not dynamic. You will also notice that if you raise the volume knob, the amplifier seems to begin to come to life, and the sound becomes saturated, filled with frequencies, becoming more dynamic and interesting. It's the end lamps that work.

Take for example the Deluxe Reverb, 22W - a classic American clean sound. But by raising the volume to 5-6, the amplifier will begin to overload and this sound will be completely different from what your overdrive pedal sounds like. You will notice that it has more overtones, the sound is fuller, richer, and more dynamic. The amp is more responsive to your playing and the volume knob on your guitar. These are the main characteristics of terminal lamp overload. When the tube in the amplifier begins to overload (so-called breakup occurs), it seems that a little compression is added to the sound along with the overdrive. It is important, however, not to forget that in our example, the tubes in the preamplifier are also partially responsible for the overload. It is the combination of overloading the preamp and end tubes that gives that delicious and magical result!

The power tube is one of the last links in the guitar sound chain. It is located in the amplifier directly in front of the output transformer. The different types of tubes in the power supply determine the sound character of your amplifier. Know that the overall sound is made up of parts. And each of these parts is very important. Preamp, equalizer, end, transformer, speakers - all these things ultimately give the sound for which we are willing to pay such crazy money. Power lamps alone do not solve anything. But today we will talk about them.

very widely used in American amplifiers, it has become synonymous with the Californian sound. These tubes are used by Fender, Mesa Boogie and many others. Of all four types of tubes discussed in this article, the 6L6 has the most spacious sound, it is more difficult to drive, and you need to make the amplifier louder. The power of one 6L6 lamp is up to 30 W, depending on the amplifier circuit. I've come across small 15W 6L6 amps, as well as 60W guys like the Hot Rod DeVille, so there are plenty to choose from.

In my opinion, the 6L6 tube has a very powerful, articulate bass - and that’s great. When we turn on such an amplifier louder, the tubes begin to overload and compress the sound, the low end becomes denser (depending on the circuit of the particular amplifier). The highs are best described by the word "sparkling." The 6L6 is a fairly bright tube overall that sometimes needs to be darkened a little. The bright highs and expressive lows give the impression that the mids are hollow. Prominent examples of this sound are the Fender Twin Reverb, Vibrolux and Blues Deluxe amps. It's a classic glassy Fender sound, and while it has a lot of headroom, the 6L6 sounds really cool when you drive it. The rich compression and vintage character of the mids and lows work well together, and the raised top end adds some edge and brightness to the sound.

Radio tube 6V6

6V6 tubes began to be produced shortly after the first release of 6L6 in the late 30s. This little brother is less powerful than the 6L6 and does not require a powerful and expensive transformer in order to work properly. Lamp output power 7-12 W. This is a great choice for home amps like the Fender Champ.

Despite having less power than the 6L6, the 6V6 is very similar. The bottom is large and voluminous, the tops are sparkling, but the lows of this particular lamp are more elastic and easier to control, and the highs are softer, they do not have the sharpness and sharpness that the 6L6 has. I also hear clearer mids. Overall, the 6V6 is a very balanced tube. The highs are bright and the mids aren't as suppressed. The attack is softer, there is a good balance of highs, mids and lows, and a calmer tone. Despite its differences with the 6L6, the 6V6 is also considered an epithet of American sound.

Radio tube EL34

The radio tube was first produced by Mullard in 1953. It has approximately the same power as the 6L6 (11-30 W). Popular amplifier models typically use a pair or quartet (4) of EL34 tubes, giving an output of 50 or 100 watts respectively. Radio tube EL34 is responsible for that very British sound. Mainly due to the fact that Marshall especially often used it in its amplifiers.

The EL34 Mullard sounds nothing like a 6L6 or 6V6. The bottom is softer, with good presence. The sound overall is not as round and voluminous, but overall has good presence. The tops are soft, transparent, not too sparkling. The middle is why everyone loves these lamps. The mids sound rich and full, but not too much. This sound fits perfectly with guitar frequencies. The sound is very rich and there is no feeling that the middle is simply raised. Everything is very balanced and fits perfectly in the pack. The ideal lamp for lead guitarists. When the EL34 is overdriven, the sound gets compressed and really starts to scream. Amazing sustain - I think this has to do with the way the tube behaves in the midrange - very dynamic. The EL34 is a great tube if you like to play loud and is very suitable for high gain situations.

Radio tube EL84

A very popular tube, it is loved by many guitarists and guitar amp manufacturers. The maximum operating voltage for the EL84 lamp is 300 Volts, and the power is 17 W; however, many manufacturers force this lamp to operate at a voltage of 400 V. As a result, these lamps are very short-lived. But unlike the other participants in the review, these lamps are the cheapest :)

The EL84 vacuum tube is the basis of the Leeds sound. Vox is responsible for this sound. The EL84 tube has its own special timbre, elastic lows, bright highs and a very interesting midrange that begins to cut through when we overload the tip. The clean sound is bright and springy, and the overdrive sounds as if the mids are deliberately turned up, while leaving a tight low end and sparkling highs. Most EL84 amplifiers seem to be made specifically to cut through the mix like a knife. And since the fashionable trend towards low-power amplifiers began. many manufacturers began to actively use EL84 in their circuits

Conclusion

So, we have covered the 4 most popular types of lamps. There are others, as well as varieties of those already mentioned above. But these 4 tubes are the basis on which the idea of ​​the sound of a tube guitar amplifier is built. Don't forget that the tubes in the end are not the whole sound. The preamp, frequency control section, transformer, speakers and all other parts are very important. Didn't you know that a red cabinet doesn't sound like a black one? Well, now you can definitely figure out what direction you want to move in to get YOUR signature sound. The article is very subjective, like any description of sound in words. Different people hear differently. The best way is to listen with your own ears. Trust only yourself!

Any music lover would like to hear the warm tube sound from his guitar, but not everyone can afford a good amplifier. This article will help you make your own tube guitar amplifier.

Some time ago, a friend of mine asked me to make an amplifier for him. I had some lamps and a CD-ROM drive, and I decided that I could help him. In the video, my friend plays the guitar with an assembled amplifier. Let's start assembling a simple tube amplifier!

Step 1: Tools

For assembly you will need:

• soldering iron
• drill
• glue gun
• drills for metal and wood of different sizes
• large drill 1.3 cm

Step 2: Materials

You will need few materials for assembly:

• power transformer that can output 277-300V
• filament transformer 6V
• switch
• powerful beam tetrode 6P6S
• 12A lamp – 7 pcs.
• CD-ROM drive
• 100k potentiometer – 2 pcs.
• 6.4mm audio jack
• 0.02 µF capacitor – 3 pcs.
• 0.002 µF capacitor
• 120uF electrolytic capacitor
• 10uF electrolytic capacitor
• resistors: 10k, 32k, 100k, 1M
• bridge rectifier
• inductive choke
• output transformer 900:4

Step 3: Prepare the CD-ROM drive

When I started building the amplifier, I was looking for something to make a metal case for it, and decided to use an old CD-ROM drive. First, remove the bottom cover and take out all the plastic parts and electronics. Now press down on the hole in the top cover to remove the piece of metal that the sticker is holding in place.

You should now have a round hole that is perfect for the tetrode. Now use a 1.3 cm drill to drill holes for the preamplifier tubes. Then we drill holes in the front wall for the switch, potentiometers and audio connector. They can be inserted into the holes provided for them.

Step 4: Mount the lamp holder

The tube holder connects the tubes to the amplifier. I decided to make the lamp holder out of wood, although you can just buy it. I painted the lamp contacts with a simple pencil and left imprints on a sheet of chipboard, these are marks for drilling holes. Then we drill these holes and glue the wires with hot glue, so that one bare end of the wire is in the hole.

Then we cut off the sides of the lamp holder as much as possible to save space inside the drive housing. Since one lamp, 6Zh4P, serves as a control lamp for switching on, it does not need a wire. In the center we make a hole for the diode. The lamp holder is ready.

Step 5: Power Supply

Follow the diagram in the picture to assemble the power supply. Since the power supply contains a miniature autotransformer, its chassis is “hot”, which makes it more dangerous than usual. For greater safety, use an isolation transformer, or a regular power transformer. Be sure to use an induction choke and a smoothing transformer to remove interference. The power source must provide a stable 300-350 V voltage at B+ and up to 6 V filament voltage.

Step 6: Making the Wiring

When connecting components, follow the diagram in the figure. To reduce the level of interference, it is better to use short connecting wires. The pinout of the lamps is also in the attached drawings. Here you can use your imagination and arrange wires and components the way you like. Just make sure that those wires that should not touch each other are not touching.

Step 7: Testing

Once assembly is complete, the amplifier should be tested. Connect it to the isolating autotransformer and gradually increase the voltage to check if there is a short circuit or smoke. If everything works fine, plug in your guitar, iPod, or banjo and listen to really loud music. Happy building!
Warning! When assembling an amplifier you are dealing with potentially lethal voltage, you do so at your own risk!

In the comments, many complained about the unsafe design, with which I completely agree. This simple amplifier can be dangerous to people unfamiliar with electrical safety. There are also complaints about the meager filling of the amplifier. It does not have a power transformer because I did not have one, and I assembled the device from what was at hand. Same with the lamp holder. Finally, this amplifier will then be built into the cabinet.

The amplifier has all the attributes of its “big brothers” - prototypes. The presence of two controls (gain and volume) allows you to flexibly redistribute the gain of the circuit cascades to suit the desired sound. To expand functionality, the amplifier has two inputs of different sensitivity, and changing the gain of the path allows you to get a sound from pure Clean to a powerful and dense Overdrive with Sustain. Equipping with an effects loop - Effects Loop - provides ample opportunities for experimenting with sound using external effects pedals or guitar processors. A two-band tone control provides deep adjustment of the amplifier's frequency response. An output switch for two nominal impedances (8 or 16 ohms) of the speaker system and a standby mode switch complete the look of the amplifier.

The amplifier was tested together with a Yamaha EG 112 electric guitar, with a set of S-S-H pickups, when working with guitar cabinets (loudspeakers) with dynamic heads measuring 6" (BCS 0608), 8" (Tesla), 10" (PSR1030), 12" (4A -32). For home use, it is better to use a speaker with a 6 or 8 inch driver, which does not create high sound pressure. In larger rooms, better results are achieved by using heads measuring 10 and even 12 inches.

In terms of nonlinear distortion, the parameters of this amplifier can be compared with the Fender Blues Junior amplifier (model 1995), which, with a power of 13 W per tone signal and a load of 8 ohms, has a harmonic coefficient of 5%, which is quite acceptable for guitar amplifiers.

Specifications

Sensitivity values ​​for both inputs are indicated taking into account the combination of switching on jumper S1 and switch SA1 (HG mode), marked in parentheses.

Description of the circuit and features of the amplifier

The circuit diagram of the amplifier is shown in Fig. 1.

Fig.1. Guitar amplifier circuit diagram

The signal supplied to input X2 (High) is sent to the low-pass filter R1C3, which helps reduce HF noise and interference, and also prevents signals from broadcast stations from penetrating the input. The signal then goes to the pre-amplification stage. It is made on a low-noise nuvistor 6С51Н-В (VL1), installed on a separate printed circuit board. To reduce the cascade's own noise, the resistance of the grid leakage resistor is reduced to 510 kOhm and the anode supply voltage is reduced. The gain of the cascade is 10. When jumper S1 is installed, capacitor C5 is connected in parallel with resistor R4 and the gain increases to 30. To eliminate the microphone effect when using input X2, the amplifier should not be placed on a speaker when operating at high power levels.

The Low input (connector X1) has lower sensitivity. The input signal is fed to the control grid of the 6N2P-EV triode (VL2.1) through the R6C6 circuit, which provides an increase in the frequency response of the amplifier in the range of 2...5 kHz. This creates a brighter sound for the instrument, known as Bright. The gain of the cascade is 50. To increase the stability of its operation, the anode load in the form of resistor R9 is shunted by capacitor 08, the capacitance of which also affects the frequency response of the amplifier.

The amplified signal from the anode load of the triode VL2.1 is fed through the isolation capacitor C9 to the gain regulator R12 - Gain. Capacitor C12, together with part of the resistor of the gain regulator, provides a rise in the frequency response in the region of 2...5 kHz, its effect stops in the upper position of the resistor slider. From the gain control the signal is supplied to the VL2.2 triode grid.

The VL2.2 triode cascade serves to amplify and compensate for signal attenuation in the tone block, and at high levels of amplified signals, to limit them. With a large gain of the previous stages and a high level of the input signal, the stage leaves the linear amplification mode - its overload and limitation of the amplified signals occur, which leads to the enrichment of the signal spectrum with harmonics and creates the characteristic buzzing sound of the Overdrive effect.

To increase the stability of the cascade at high frequencies, the anode load of the triode is shunted with a small capacitor, which also affects the frequency response of the amplifier in the high frequency region. The cascade gain is selected using switch SA1. When its contacts are open, the gain is 20, when closed - 48. To eliminate loud clicks during switching, resistor R15 is used, which ensures the flow of charging current to capacitor C13.

The signal from the anode load R17 through capacitor C17 is supplied to the tone control. The separation of the bass and treble control bands is in the region of 600...800 Hz. With the tone control knobs in the middle position, the block gain is approximately -22 dB. To limit the spectrum of amplified signals, a low-pass filter R29C21 is installed in the path; it determines the decrease in gain in the region of higher frequencies and filters out “non-musical” components of the spectrum. This has a beneficial effect on sound clarity when working with Overdrive. The high-impedance output of the tone block is connected to the input of the source follower on the field-effect transistor VT1, which eliminates the influence of the cascade on the operation of the tone block.

To expand functionality, the amplifier has a built-in “effects loop” - Effects Loop. The signal to external devices (effects pedals, guitar processor) is removed from resistor R13 of the source follower on transistor VT1 and through capacitor C16 goes to the level control R19 (X3 Send). To ensure the necessary load capacity of this output, the quiescent current of the transistor is set to 4 mA. The low output impedance of the cascade reduces the influence of the capacitance of the connecting cable and ensures normal operation with devices with an input impedance of at least 10 kOhm. Processed by external devices, the return signal is fed through the X4 Ret connector to the R26 level control. Input impedance at the Ret input is 50 kOhm, sufficient for connecting external devices with increased output impedance. The presence of controls allows you to optimize the input and output levels of signals in the effects loop. If you exclude the elements of the effects loop, the resistance of resistor R30 must be increased to 1 MOhm, and the signal from the output of the low-pass filter R29C21 must be applied to the volume control resistor R30.

In the absence of external devices included in the effects loop, the signal from the output of the source follower through the volume control R30 (Master volume) is supplied to the input of the bass reflex stage, which generates paraphase excitation signals of the push-pull output stage. The different AC switching of the two phase inverter triodes causes a slight difference in the amplitude of the signals at the anode load resistors. Their alignment is achieved by selecting resistor R39. The gain factor of the bass reflex stage is 24.

The final stage (VL3, VL4) is made according to a push-pull circuit using beam tetrodes of 6F3P combined lamps, their triode parts are used in the bass-reflex stage. The final stage lamps operate with a fixed bias in AB1 mode, i.e. without grid currents. This bias makes it easy to optimize the operating mode to obtain maximum output power with higher efficiency while tolerating non-linear distortions.

Using the lamp quiescent current balance regulator (R40), it is possible to compensate for the spread in the modes of the lamps used to reduce nonlinear distortions and eliminate magnetization of the transformer magnetic circuit by the difference current of the lamps. Resistor R33 regulates the bias voltage, setting the required quiescent current of the lamps.

The quiescent current of the lamps (2x30 mA) is set by monitoring the voltage drop across the cathode resistors R47 and R48. Their resistance is 1 Ohm (deviation no more than ±1%). The voltage drop across these resistors, measured in millivolts, is numerically equal to the sum of the lamp's anode and screen grid currents, expressed in milliamps. The supply voltage for the anodes and screen grids of the final stage lamps is supplied through a damping resistor R53, which, together with capacitor C41, forms a filter that reduces the level of ripple in the supply voltage of the final and phase-inverted stages.

The power supply is built using a network transformer, which is relatively low voltage for such devices. The required anode supply voltage is generated by a rectifier with doubling the voltage on diodes VD4, VD5. To obtain a voltage of -47 V (for grid bias) and +49 V (for a stabilizer with an output voltage of +9 V), an alternating voltage from one section of the anode winding (-27 V) is used. During operation, the anode winding acquires a potential relative to the common wire of approximately +130 V, therefore, to “decouple” the rectifier bridge VD2, capacitors C32, C34 are introduced. In addition, this option of connecting diode bridges allows you to get almost double the rectified voltage. A similar role is played by oxide capacitors C31, C35 in a bias voltage rectifier with a diode bridge VD3. During installation, it is necessary to pay attention to the polarity of these oxide capacitors, since violation of this polarity will lead to their overheating and destruction.

The required current to power the lamp heaters is achieved by parallel connection of all filament windings of the transformer. The VD6 rectifier bridge with capacitor C42 provides DC power to the filament lamps VL1 and VL2, which virtually eliminates the 100 Hz hum.

To extend the service life of the lamps, the anode power should be turned on after warming up the cathodes of the lamps, and during breaks in the operation of the amplifier, it is advisable to turn off the anode power with switch SA4 (Stb).

The anode power to the phase inversion and preliminary stages is supplied through inductor L1, which, together with capacitor C26 and RC filters R5C1, R25C18, effectively suppresses supply voltage ripple.

Construction and details

The chassis is made of galvanized iron with a thickness of 0.6...0.8 mm. The advantage of this design is the availability of material and ease of manufacture at home. This chassis effectively shields the amplifier stages from magnetic and electric fields, has a pleasant appearance and is not subject to corrosion. A chassis blank with dimensions for the amplifier installation components is shown in Fig. 2. Dimensions (HxLxW) - 50x280x150 mm.

Fig.2. Tube Guitar Amplifier Chassis Drawing

After cutting the workpiece, even before bending, it is necessary to make all the holes for the installation elements. Then, at the bend points, on the inside of the chassis, using a cutter made from a hacksaw blade, using a metal ruler, make grooves with a depth of approximately 1/3...1/2 of the thickness of the metal, this will allow you to easily and evenly bend the chassis at the edge of the table. Solder the joints of the walls in the corners along the entire height. Additionally, brass posts with a diameter of 8...10 and a length of 6...10 mm with M3 threads are soldered into the corners of the chassis, this provides additional strength and rigidity of the entire structure. Subsequently, the bottom cover of the chassis is attached to these racks.

All printed circuit boards are made of foil fiberglass laminate with a thickness of 1.5 mm.

A drawing of the printed circuit board and the location of the pre-amplifier elements on the Nuvistor (VL1) are shown in Fig. 3 (rectangular holes for flat connector pins are formed by drilling with a drill collar). A drawing of the printed circuit board and the location of the elements of the bias voltage source and stabilized voltage +9 V are shown in Fig. 4. Similar drawings for the effects loop board are shown in Fig. 5, and for the output jack board for connecting acoustics and a protective resistor - in Fig. 6 (opening contacts are connected in parallel).

Fig.3. Preamplifier PCB Drawing

Fig.4. Bias Voltage Source PCB Drawing

Fig.5. Effects loop PCB drawing

Fig.6. Output Jack PCB Drawing

Decorative front and rear panels are made of 1.5 mm thick aluminum. Their dimensions are 280x60 mm.

The housings of oxide capacitors C18, C26, C39-C41, C43 are insulated with a heat-shrinkable tube. Capacitors C26, C41, C43 are fixed with tin plate clamps on aluminum plates 1.5 mm thick. The plates are mounted on tubular stands 10 mm high, with holes for transformer mounting screws.

Choke L1 is made from a TAG type subscriber loudspeaker transformer. Its new winding is wound with PEL-0.15 wire until the frame is filled. The cross-section of the magnetic circuit is 12.7x5.3 mm with a core height of 15 mm, although it is acceptable to use any other one with a large core volume. The plates are assembled side by side, without a non-magnetic gap; at low current values ​​this is acceptable. Inductance L1, measured without bias current, is 10 H, the active resistance of the winding is 145 Ohms.

Most of the amplifier parts are mounted using vertical mounting posts. To accommodate a number of elements that have terminals connected to a common wire, it turned out to be very convenient to use mounting strips 4...5 mm wide, made of foiled fiberglass laminate. The foil around the holes for the screws for fastening the strips has been removed. On the bar where the parts of the cascade with the VL2 lamp are mounted, pads are additionally cut into the foil for soldering parts connected by wires to other components; you can see it in the photo. The numbering of the lamp terminals indicated in the diagram is most convenient for installing the cascade. For power distribution of incandescent lamps VL1, VL2, a twisted pair of single-core wires with a diameter of 0.5...0.6 mm is made. The filament power supply for the final stage lamps is made with MGShV-0.35 twisted wires.

The pre-amplifier board output is connected to the VL2.1 triode stage using a shielded wire. The screen braid is soldered to the petals at both ends and connected to the chassis.

Capacitor C39 is installed on the chassis on insulating bushings. Its body is under voltage equal to half the anode voltage.

To prevent damage to the output transformer when the amplifier is turned on without a load, use a load resistor R54 with a power of 5 W (PEV or imported type SQP for 5-10 W) and a resistance of 20...30 Ohms. Filter resistor R53 (PEV 7.5 - PEV 10) is installed in the basement of the chassis. It also limits the pulse of the charging current of the capacitors when the anode voltage is turned on.

Fixed resistors of the effects loop boards and sources are +9 V and bias - MLT-0.25. The rest are MLT-0.5 or imported MF. It is acceptable to use some resistors and less power (see diagram). Variable resistors R12, R18. R28, R30 - SP-P or SP3-30, with an inverse logarithmic dependence of the change in resistance on the angle of rotation (group B). The use of group A resistors (with linear dependence) for regulators is undesirable; this will make it difficult to control gain and volume, especially at low levels, and will make the tone adjustment rough. The resistance of resistor R30 can be increased to 470 kOhm or more. The metal covers of variable resistors R12, R18, R28, R30 must be connected with a wire to the chassis. The housings R19, R26 of the effects loop board are also connected by a conductor (under the nut) to the common wire of the board. Trimmer resistor R40 - wire PP2-11, PP3-11 or PPB-1 B. Trimmer resistors R19, R26, R33 - SP4-1 with a power of 0.5 W. Resistor R53 - PEV with a power of 7.5 or 10 W.

Capacitors C26, C41, C43 are oxide K50-27. Capacitors C39, C40 - K50-12. Permanent capacitors in the anode and grid circuits of cascades must have minimal leakage currents. You can use film or paper K73-17, K40U-9, BMT-2 and the like for a voltage of 400-630 V. Capacitors C32, C34 - K73-16V, possible replacement - K73-14. Capacitors in the tone block - K10-17.

Switch SA1 - toggle switch MT-1, switch SA3 - toggle switch MT-3. Switches SA2, SA4 are imported with a built-in indicator lamp (ballast resistors in the neon lamp circuit are not shown in the diagram). Connectors X1, X2, X5 - Jack 6.35 mm (ST-020) with two pairs of open contacts, connectors X3, X4 - with three pairs.

6N2P-EV lamps can be replaced by any of its modifications, and 6S51N-V lamps can be replaced with any Nuvistor triode (with some mode correction). When setting the anode currents of lamps of preliminary stages operating at low signal amplitudes, it is not advisable to increase the anode current above 1 mA; this will not improve their operation.

The network unified TPP252-127/220-50 is used as an output transformer; it is also possible to use an incandescent TN33-127/220-50. In this case, it is necessary to recalculate the transformation coefficient of the windings. The power supply uses a network anode-heat transformer TAN 1-220-50. The best replacement for it would be TAN 13-220-50 (without changing the switching circuit).

LITERATURE

1. Tsykina A.V. Electronic amplifiers. - M.: Radio and communication, 1982.

V. Ovsyannikov, Perm

Magazine "Radio" 2012, No. 2-3

Hi all! Since I am a musician, the issue of audio equipment concerns me very, very much! Well, as you know, one of the most important parts of the sound path of an electric guitar is the amplifier. Either a head with a cabinet or a combo.

Since I had a transistor amp with a guitar speaker, I decided not to touch it, but to assemble a separate push-pull tube amplifier, i.e., the head. The amp had a microcircuit filling (in general, not bad for clean sound and light crunch), but I wanted to try the “live” tube sound. So it came to the Marshall 18 Watt. Here is the original diagram with my amendments:

Together with colleagues, soldering musicians, consultations were held on the design, and the process began :) Since I needed the amplifier for home recording, I did not need all its power. It’s decided - we’ll simplify the scheme! I reduced the values ​​of the pass capacitors, for example, from 47 nF to 1 nF - this made it possible to significantly reduce the low frequencies in the signal spectrum and, thereby, the overall output level of the amplifier. You can leave the original capacitance of 47 nF if you want more level. As a result of simplifications, the following diagram was obtained:

Attention! This build is amateur! Claims for literacy in electronic theory and practice will certainly have a basis and will be accepted - this will help others avoid mistakes in design. Don't judge strictly, if anything!

You must understand that you use amateur builds at your own peril and risk. There is no guarantee that there will be no errors! If you want guaranteed sound, try to stick to the original design and buy high-quality components!

For the chassis, it was decided to use an old U-shaped computer case, which is very convenient. So, let’s arm ourselves with safety precautions and an angle grinder:

Dimensions of the workpiece for the chassis: width - 18 cm, length - 45 cm, height - 6 cm. Since the transformers are quite large, the decision was made to “sink” them into the chassis:

We model the arrangement of components on the chassis and make guide cuts with a grinder:

Next we make holes for the lamp panels. Of course, I did it clumsily :) I drilled small holes around the circumference, then bit them out with wire cutters and sharpened them with a file... If you have the opportunity, then drill the holes with a metal core bit with a diameter of 22 mm. It will be fast and beautiful! Let's try on:

The arrangement of lamps is as follows:

Let's bend the iron :) By the way, next to the power switch there will be an indicator - an ordinary light bulb from a flashlight 6.3 V x 0.3 A. This is where the second weak incandescent winding of the power transformer comes in handy. I make an insert from the chipboard at the end. Then I’ll add a metal corner to it and fasten them from below with plywood:

At the same time I make a circuit board (20x4 cm). In the picture you can see two crossed out parts - don’t be alarmed, I turned off the Tone control, and these parts were connected to the potentiometer. If you need tone, then don't pay attention to it. Then there will be a drawing with the wiring.

It's time for installation. Let's look at the assembly diagram:

Capacitors in power and signal circuits must be designed for an operating voltage of at least 400 V! In cathode circuits it is possible at 50 V. I set the pass capacitors at 1 nF to reduce low frequencies and, thereby, reduce the amplifier level. After testing, I removed the tone altogether - it turned out to be not needed, it is on both the guitar and the gadgets. I installed the resistors that came to hand - with a power of 0.125 and 0.25 W. Well, it’s mandatory to select the powerful ones (in the power supply circuits), otherwise the weak ones will be zapped at once! I managed to mix up the polarity of the diodes - the filtering electrolytic capacitor “crunched” and died! Do as in the diagram - stripes where stripes are!

And of course, photos of the installation itself:

To ensure safety and a more or less aesthetic appearance, I decided to make protective covers for the transformers and inductor:

The output transformer TS-250-2M was taken from an old Soviet TV. Option for connecting windings in the image. The input winding is tapped from the middle at 190 V. The output winding (to the speaker) is 6.4 V 0.9 A (essentially filament).

The location of the terminals of the TS-250-2M transformer is indicated on its reverse side:

The power transformer was also taken from an old TV - this is TSSh-170-3 (diagram attached). Two secondary windings total about 200 V - after rectification - 250 V. Incandescent - 6.3 V x 3 A - enough for all lamps, and another incandescent less than 1 Ampere - suitable for a network indicator light.

IMPORTANT!!! Helpful notes! Take into account!

1. A colleague advised to use 6N23P instead of 6N2P. For which he has great respect! I checked this case - and sure enough! The sound became noticeably richer in the upper frequencies and the crackling distortion went away (otherwise the microphone had to be moved almost half a meter away from the amp). SUMMARY: 6N2P is definitely for retirement, and 6N23P is on Marshall 18 Watt and Fender Tweed Deluxe 53D. Here's a sample as proof:

2. In my version of the amplifier, both inputs of the input tube are paralleled, which is not usually done! This overloads the output stage. If you want, try this. But in fact, it is better to use one half of the input lamp, as it should be.

3. To ensure reliable background suppression, add filtering electrolytic capacitors in the anode circuits of the first and second lamps. Their ratings are 16-32 µF / 450 V. The original has them, I tried without them - there was no background, so I removed them to simplify the circuit.

Field tests.

The reduced volume (as a result of the lighter circuit) is enough for home recording! A push-pull amplifier sounds brighter (more vocal, etc.) than a single-ended amplifier. Naturally, this is the case with a guitar; we don’t understand audiophile nuances! The amplifier works well with the BOSS Metal Zone MT-2 pedal :) The background is defeated, no problems. A slight hiss of white noise, but compared to the signal level of the guitar - dust! Just for fun, I turned off the throttle - oh no, the background appeared! Low-budget guitar Cruzer by Crafter ST-200\BK.

Here are some simple game samples, no effects processing was performed. BOSS MetalZone MT-2 pedal. I added highs and mids to the distortion solo.

Clear sound. Arpeggio:

Clear sound. Rhythm:

Distortion Rhythm:

Distortion Solo:

We draw conclusions from my experiment:

1. Making a tube amplifier for a guitar at home is quite possible! My experience proves this!

2. If your budget is limited, then you can pick up parts literally from remnants of the Soviet past :)

3. If you have some money, you can buy high-quality transformers and lamps. The sound will be excellent! And the cost will be several times cheaper than the original amplifier!

P.S. Sorry, I'll repeat it! Please consider this project as an amateur home experiment. There may be errors, mistakes, terminological inaccuracies, etc. Take a closer look at the original diagram and figure out what's what. Consult with experts. Don't rush into making a decision, the main thing is that it is right for you! And then everything will work out for you! See you!